There are a bunch of threads describing our journeys from the Texas border to Playa.
If you are going to make this journey, I would take a look at that search tool and do some reading first.
I personally recommend avoiding Mexico City on this type of journey. Many people do end up lost, and it is not the best place to be looking like a tourist and asking for directions; perhaps at night. We also avoid the last leg of the journey into Q Roo via Merida simply because of the toll roads. Note: we do very much like both of these cities and recommend visits as tourists; we just don’t like to include them in a long journey that has other possible complications. But then again if you have the time, go for it.